1. Field of the Invention
This invention relates to a work mounting apparatus for mounting IC chips or like electronic components, as works, on printed boards.
2. Description of the Related Art
A work mounting apparatus of this type is disclosed in U.S. Pat. No. 5,234,304, for example. This conventional apparatus comprises a circular worktable, a head drum arranged above the worktable for continuous rotation and having pivots extending in a radial direction thereof, respectively and a plurality of work heads projecting from the outer periphery of the head drum. Each work head is capable of turning around the pivot of the head drum while maintaining a fixed orientation with respect to the worktable, and a suction nozzle projects from the outer peripheral surface of each work head toward the worktable. The worktable has a work supply section and a work mounting section, which are arranged below the path of movement of the work heads and separated from each other in the circumferential direction of the worktable. The work mounting section is supplied with printed boards.
The supply section of the worktable is provided with a number of work feeders disposed in radial form. The work feeders are capable of continuously supplying various electronic components, e.g., IC chips, resistors, capacitors, etc., as works, to respective supply positions on the worktable.
The work mounting section is provided with an XY table, on the upper surface of which are supplied the printed boards on which the works are to be mounted.
In the work mounting apparatus described above, as the work heads turn around their pivot during rotation of the head drum, the suction nozzle of each work head moves in the circumferential direction of the worktable, i.e., along the path of movement of the work heads, while making cycloidal motions. By appropriately setting the turning direction and speed of the work heads with respect to the circumferential speed of the head drum, the speed of the suction nozzle of each work head relative to the supply and mounting sections can be made zero at the time when the suction nozzle approaches closest to a supply position on the worktable and the printed board, that is, when the suction nozzle is at its lowest position. Consequently, even while the head drum is continuously rotated, the suction nozzle of each work head is able to reliably suck up a work on the supply position. The work retained by the suction nozzle moves, together with the work head, to the mounting section, and then is mounted to a printed board on the mounting section.
In order for the work to be accurately mounted at a target point on the printed board, it is necessary that the XY table move the printed board such that the target point on the printed board is set at the path of movement of the work heads, i.e., the path of movement of the suction nozzles, and also that the movement of the printed board be completed before the work retained by the suction nozzle of the work head reaches a position above the printed board.
To improve the efficiency of mounting works on the printed board, on the other hand, the rotational speed of the head drum, i.e., the moving speed of the work heads, need only be increased. In this case, however, a disadvantage arises in that sufficient time cannot be saved for the movement of printed board, and thus the work mounting efficiency is restricted by the capability of the XY table itself. More specifically, the suction nozzles of the work heads successively pass above the printed board on the mounting section; therefore, after one work head passes above the printed board the operation of the XY table must be completed before the next work head reaches the printed board. If the speed of revolution of the work heads is too fast, the operation of the XY table fails to follow the work head speed.